1. Field of the Invention
A light emitting device module consistent with the present invention includes a plurality of light emitting devices, and achieves a reduced thermal influence on the light emitting devices.
2. Description of the Related Art
Light emitting device modules are widely used in projectors, displays, indicators, traffic lights, and lighting devices. Related light emitting device modules emit white light or colored light by combining light emitting devices having different wavelengths, and increase the brightness of the light by using solid light emitting devices, such as light emitting diodes (LEDs).
In these light emitting device modules, in order to avoid the influence of self-heating when emitting light, each light emitting device is arranged separately on electrodes or a substrate.
As an example of such a light emitting device module, Japanese Patent No. 3329716 (hereinafter, Cited Reference 1) discloses a light emitting device module which includes chip type LEDs, on which LED chips, each emitting green, red and blue light, are arranged on a common electrode. The size of the common electrode may be maximized according to radiating properties or reflectivity. Referring to FIG. 1 of Cited Reference 1, the distance between adjacent LED chips, which have an approximately square shape, is obviously greater than one side of the square.
Japanese Patent Publication No. 2005-159262 (hereinafter, Cited Reference 2) discloses a light emitting device module which includes at least three approximately square-shaped light emitting devices arranged at similar intervals on a body formed of resins, such as ceramics and epoxy, and a light transparent member covering the light emitting diodes. The interval between adjacent light emitting devices is the same or greater than one side of the approximate square.
These related light emitting device modules have the following problems.
In Cited References 1 and 2, since a plurality of adjacent light emitting devices are separated at an interval greater than a size of a light emitting surface of each of the light emitting devices on a radiating member, such as electrodes or a substrate, the light emitting devices are cooled by radiating of the radiating member. However, a radiating amount is increased. Therefore, the light emitting devices are likely to have a thermal influence on each other. For example, a poor luminous efficiency decreases the brightness or lifetime of the light emitting devices.
In order to avoid a thermal influence, a radiating member should be large, or arranged in a wide interval. Thus, arranging light emitting devices adjacent to each other causes problems.
In a light emitting device module which includes a plurality of light emitting devices arranged at specific intervals to each other, when one optical system focuses light emitted from each device, the light efficiency is poor or an aberration is worsened when the light emitting devices are arranged on a line that is slightly off the axis of the optical system. For example, when a plurality of light emitting devices are used in order to improve brightness, light efficiency may be poor. In addition, when colors are indicated by using light having a plurality of wavelengths, color spots may occur.